UNDERSTANDING AND EXPLOITING MULTIMODE FIBER DISPERSION

Multimode fiber (MMF) is widely used in short-reach systems, such as data-center networks. Random perturbations cause coupling between modes having different group delays (modal dispersion), strongly limiting bit rate ´ distance products (to about 10 Gbit/s ´ 300 m in current systems). For decades, modal coupling and dispersion have been modeled using incoherent power coupling models. By using a coherent field coupling model, we predicted the existence of principal modes, which are linear combinations of ideal modes that are free of modal dispersion to first order. As random mode coupling evolves over time, the principal modes and their delays change. Using adaptive optics to launch into a principal mode, we have achieved transmission far beyond previous bit rate ´ distance limits (10 Gbit/s ´ 11 km or 100 Gbit/s ´ 2.2 km). We will discuss further increasing transmission capacity in short-reach MMF systems by spatial multiplexing in several principal modes. Finally, we will discuss spatial multiplexing in MMF to increase capacity in long-haul systems using inline optical amplifiers and coherent receivers. Mode-dependent gain poses serious challenges, which we hope to overcome by exploiting innate properties of multimode propagation.

Speaker:  Joseph M. Kahn, E. L. Ginzton Laboratory, Department of Electrical Engineering, Stanford University

Room 115